Emerging Requirements for Electronic Materials Product Quality and Metrology
In order to keep pace with Moore’s Law, semiconductor market leaders have had to adopt increasingly challenging technology roadmaps, which are leading to new demands on electronic materials (EM) product quality for leading-edge chip manufacturing.
Critical process steps in high-volume semiconductor device manufacturing at aggressive feature sizes require stringent control of variability. For a silicon wafer with 100 or more advanced logic chips, each with up to 4 billion transistors and billions of connections:
- Essentially all the transistors and connections have to work as intended on each chip and
- The process has to be repeatable from wafer to wafer while chip production proceeds at rates of up to 50,000 wafer starts per month through a fab!
Variation among otherwise identical transistors on a chip will lead to poorer overall chip performance and must be minimized. This issue is exacerbated by the fact that critical feature sizes on the latest semiconductor devices are now several thousand times smaller than the thickness of human hair.
Variation in the form of a process excursion—when something unexpected happens in the manufacturing process—can also be very expensive. A starting wafer has a typical cost of $120. After the wafer has been subjected to several hundred process steps over a period of six to eight weeks, the investment in the finished wafer can be of the order of $1,000 to $4,000. However, based on the selling price of the chips, this same finished wafer can represent a value of as much as 10 times the processing cost in terms of the revenues it can bring in for the chip maker!
Major industry players have pointed out that even trace contaminants—including those that are not specified on a standard Certificate of Analysis—can cause measurable shifts in semiconductor processes and affect chip performance as device geometries continue to shrink. There can sometimes be a lag of several days to weeks in the detection of problems during wafer processing. Small problems not detected early in the supply chain of the IC chip fab will increase exponentially in impact as value is added during wafer processing and can reportedly cause lost revenues of hundreds of millions of dollars in a worst-case scenario.
Given that EM products are a critical input in wafer processing, it is easy to see how the quality of EM products becomes increasingly important for chip manufacturers at leading technology nodes. Apart from focusing on major assay components, which are the impurities detailed in a Certificate of Analysis (CoA), some customers are also asking that minor assay components or other trace impurities must be controlled for critical materials used in advanced device manufacturing. EM suppliers usually only look for specified impurities and do not carry out a broad spectrum analysis due to the additional costs involved.
The need for tighter and more extensive control on gas purity now demands broad spectrum characterization. When carried out on product to be supplied to a customer, such “fingerprinting” can help us detect and measure impurities not formally specified on the CoA, but which could be present in the EM product and impact IC chip manufacturing processes where the EM product will be used. Broad spectrum characterization is also sometimes required to be carried out reactively in more of a forensic setting, e.g. when something goes wrong with a product during its use in a fab.
Thus, technology changes in semiconductor processing and demands for higher-purity and better-characterized electronic materials have driven the need for advanced analytical metrology. These and related changes are shown in the evolving roadmap of EM product quality below.
In response to these stringent emerging requirements, Linde Electronics is expanding its analytical capabilities to enable broad spectrum characterization of EM products.
In addition to the need for more advanced analytical technology, the EM supplier community is focusing on implementing a robust overall process control management system that leverages tools such as Statistical Quality Control (SQC), Statistical Process Control (SPC), measurement system analysis (MSA), and automated laboratory information management systems (LIMS) in response to the evolving customer requirements to control variability.
As seen above, a full understanding of the electronic materials supply chain is required for successful introduction of new EM products and for their continued use in critical manufacturing steps in a fab. Achieving this also requires collaboration and trust between the supplier and the fab customer.
This blog post was contributed by Dr. Atul Athalye, Head of Technology, Linde Electronics.